Genetic Studies of the Proliferation versus Meiotic Development Decision

Jessica Amrozowicz Kerins1, Dave Hansen2, Laura Berry1, Daimon Simmons1, Tim Schedl1
1
Washington University School of Medicine, Department of Genetics, 4566 Scott Ave., St. Louis, MO 63110
2
Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4

GLP-1 is a member of the Notch family of transmembrane receptors and functions to promote germ cell proliferation in C. elegans. Activation of the GLP-1 receptor, expressed in the germline, is spatially regulated by the transmembrane ligand, LAG-2, expressed in the distal tip cell. Binding of LAG-2 to GLP-1 is presumed to induce receptor cleavage generating GLP-1(INTRA), which then translocates to the nucleus, binds LAG-1, and alters the pattern of transcription. Disruption of this pathway causes all proliferating germ cells to prematurely enter meiosis. Conversely, constitutive activation by the glp-1(oz112) gain-of-function (gf) mutation results in the formation of a germline tumor where proliferative cells are found throughout the gonad. Two genes, gld-1 and gld-2, function redundantly downstream of GLP-1 to inhibit proliferation and/or promote meiotic development. glp-1 signaling, in effect, inhibits both genes to promote germ cell proliferation.

We have taken a forward genetic approach to identify genes that either function downstream of GLP-1 to promote entry of germ cells into meiosis, or that function to negatively regulate GLP-1 signaling. A number of screens have been conducted in sensitized backgrounds in order to identify mutations that confer a synthetic tumorous (Syt) phenotype. One of the first screens utilized a very weak glp-1(oz112oz120 gf) background and identified mutations in the genes teg-1 and teg-4. gld-2; teg-1 and gld-2teg-4 are also tumorous. Interestingly, in contrast to the gld-2gld-1; glp-1(null) triple mutant, which is tumorous, gld-2; glp-1teg-1 and gld-2teg-4; glp-1 triple mutants display the Glp premature meiotic entry phenotype. Another screen using a teg-1 mutant background identified two weak glp-1(gf) mutants, oz264 and oz274; molecular lesions are located in the second and third LNG repeats, regions where other glp-1/lin-12(gf) mutations have been localized. Finally, another screen utilized the glp-1(oz264 gf) mutant background, which identified one Syt mutant, oz273. It appears to be associated with a Mog (masculinization of the germline) phenotype in the glp-1(+) background, similar to teg-1. Also similar to teg-1, the gld-2oz273 mutant is tumorous, suggesting that teg-1 and oz273 could be functioning in the same pathway to regulate glp-1. The oz273 mutation maps on LG1, and SNP mapping is currently underway identify the gene defined by the mutation.